The present invention relates to a pulse wave inverter circuit apparatus for producing a pulse wave output by turning on and off four transistors which are connected in the form of a bridge by a single switching signal. The circuit in accordance with the present invention is particularly suitable for, but not limited to, a driving circuit for a brushless electric motor.
An inverter circuit is known as disclosed in Japanese Utility Model Publication No. 58-47833, published Oct. 31, 1983, in which four NPN transistors are connected in the form of a bridge circuit and the transistors are controlled on and off by a signal from a switching controller so that a pulse wave output is produced. The known circuit device as described, however, has a problem in that the transistors are separately controlled. In the known circuit, it is necessary that the switching controller produces four different switching signals for separately supplying the respective transistors. Consequently, a complex structure in the switching controller is unavoidable as well as a great number of parts and elements and, therefore, it has been difficult to miniaturize and simplify the entire structure of the inverter circuit device. Besides, the bridge circuit as disclosed in the Japanese Utility Model Publication necessitates the providing of drivers on output stages of the switching controller if each transistor is modified so as to increase its current capacity so as to control a larger output of electric current, which inevitably results in a serious problem of a further complex structure of the electric circuit.